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  <xs:element id="mg_OfficeFurnitureAndEquipmentMember" abstract="true" name="OfficeFurnitureAndEquipmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_AccruedSalariesWagesAndEmployeeRelatedBenefitsCurrent" abstract="false" name="AccruedSalariesWagesAndEmployeeRelatedBenefitsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_AccruedWorkersCompensationAndHealthBenefitsCurrent" abstract="false" name="AccruedWorkersCompensationAndHealthBenefitsCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_OtherLongTermDebtMember" abstract="true" name="OtherLongTermDebtMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_TermALoanFacilityMember" abstract="true" name="TermALoanFacilityMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_CreditAgreementMember" abstract="true" name="CreditAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodAxis" abstract="true" name="DebtCovenantPeriodAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="mg_DebtCovenantPeriodDomain" abstract="true" name="DebtCovenantPeriodDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodOneMember" abstract="true" name="DebtCovenantPeriodOneMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodTwoMember" abstract="true" name="DebtCovenantPeriodTwoMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodThreeMember" abstract="true" name="DebtCovenantPeriodThreeMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodFourMember" abstract="true" name="DebtCovenantPeriodFourMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DebtCovenantPeriodFiveMember" abstract="true" name="DebtCovenantPeriodFiveMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
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  <xs:element id="mg_VariableRateComponentDomain" abstract="true" name="VariableRateComponentDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_VariableRateComponentMember" abstract="true" name="VariableRateComponentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityInNonUSCurrencies" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" abstract="false" name="LineOfCreditFacilityMaximumBorrowingCapacityAvailableForIssuanceOfLettersOfCredit" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantConsolidatedDebtLeverageRatioLowestAvailableMarginApplicable" abstract="false" name="DebtInstrumentCovenantConsolidatedDebtLeverageRatioLowestAvailableMarginApplicable" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantConsolidatedDebtLeverageRatioMaximumMarginApplicableIfGreaterThan" abstract="false" name="DebtInstrumentCovenantConsolidatedDebtLeverageRatioMaximumMarginApplicableIfGreaterThan" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantComplianceTotalConsolidatedDebtLeverageRatio" abstract="false" name="DebtInstrumentCovenantComplianceTotalConsolidatedDebtLeverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantFixedChargeCoverageRatio" abstract="false" name="DebtInstrumentCovenantFixedChargeCoverageRatio" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantNumberOfDaysBeforeBusinessAcquisitionWrittenNoticeRequired" abstract="false" name="DebtInstrumentCovenantNumberOfDaysBeforeBusinessAcquisitionWrittenNoticeRequired" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DebtInstrumentCovenantThresholdBusinessAcquisitionMinimumAmount" abstract="false" name="DebtInstrumentCovenantThresholdBusinessAcquisitionMinimumAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_LongTermIncentivePlan2016Member" abstract="true" name="LongTermIncentivePlan2016Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_InterimPresidentAndCEOMember" abstract="true" name="InterimPresidentAndCEOMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodAfterEndOfEmployment" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodAfterEndOfEmployment" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_ShareBasedPaymentAwardExpirationPeriodUponEndOfService" abstract="false" name="ShareBasedPaymentAwardExpirationPeriodUponEndOfService" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_UnrecognizedShareBasedCompensationExpense" abstract="false" name="UnrecognizedShareBasedCompensationExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_ExecutiveAndSeniorOfficersMember" abstract="true" name="ExecutiveAndSeniorOfficersMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPercentage" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardPerformancePeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardMetrics" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAwardMetrics" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNet" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNet" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="mg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNetWeightedAverageGrantDateFairValue" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsPerformanceConditionAdjustmentsNetWeightedAverageGrantDateFairValue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="mg_DeferredIncomeTaxExpenseBenefitNet" abstract="false" name="DeferredIncomeTaxExpenseBenefitNet" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLossesRecoveryAmount" abstract="false" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLossesRecoveryAmount" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLossesRecoveryPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLossesRecoveryPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="mg_OperatingLossCarryforwardsSubjectToExpiration" abstract="false" name="OperatingLossCarryforwardsSubjectToExpiration" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_TaxCutsAndJobsActTransitionTaxForAccumulatedForeignEarningsLiability" abstract="false" name="TaxCutsAndJobsActTransitionTaxForAccumulatedForeignEarningsLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DeferredTaxAssetsFinanceLeaseObligation" abstract="false" name="DeferredTaxAssetsFinanceLeaseObligation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DeferredTaxAssetsDeferredTaxExpenseStockOptions" abstract="false" name="DeferredTaxAssetsDeferredTaxExpenseStockOptions" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DeferredTaxAssetsInterestCarryforwards" abstract="false" name="DeferredTaxAssetsInterestCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_DeferredTaxAssetsOperatingLeaseLiabilities" abstract="false" name="DeferredTaxAssetsOperatingLeaseLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_UnrecognizedTaxBenefitsOtherIncreaseDecrease" abstract="false" name="UnrecognizedTaxBenefitsOtherIncreaseDecrease" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="mg_BoilermakersandPipefittersPlansMember" abstract="true" name="BoilermakersandPipefittersPlansMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderInternalRevenueServicesLimits" abstract="false" name="DefinedContributionPlanMinimumAgeForEmployeesToContributeCatchUpContributionsUnderInternalRevenueServicesLimits" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan" abstract="false" name="DefinedContributionPlanContinuousServicePeriodAfterWhichEmployeesBecomeEligibleToParticipateUnderPlan" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod" abstract="false" name="DefinedContributionPlanEmployersMatchingContributionAnnualVestingPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="mg_MultiemployerPlanPensionSignificantFundedStatusPercentage" abstract="false" name="MultiemployerPlanPensionSignificantFundedStatusPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:pureItemType"/>
  <xs:element id="mg_InsuranceConsultingAndBrokerageServicesMember" abstract="true" name="InsuranceConsultingAndBrokerageServicesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_OperatingLeaseArrangementMember" abstract="true" name="OperatingLeaseArrangementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="mg_CashFlowLesseeAbstract" abstract="true" name="CashFlowLesseeAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" abstract="true" name="RightOfUseAssetObtainedInExchangeForLeaseLiabilityAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_WeightedAverageRemainingLeaseTermAbstract" abstract="true" name="WeightedAverageRemainingLeaseTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="mg_WeightedAverageDiscountRatePercentAbstract" abstract="true" name="WeightedAverageDiscountRatePercentAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
</xs:schema>
