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    <element id="posc_OperatingLeaseTermOfContract" name="OperatingLeaseTermOfContract" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="posc_OperatingLeaseTerminationCost" name="OperatingLeaseTerminationCost" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_PreferredStockDividendRights" name="PreferredStockDividendRights" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="posc_PreferredStockLiquidationPreferences" name="PreferredStockLiquidationPreferences" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="posc_PreferredStockRedemptionRights" name="PreferredStockRedemptionRights" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WarrantsIssued" name="WarrantsIssued" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsGrantedWeightedAverageRemainingContractualTerm2" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsGrantedWeightedAverageRemainingContractualTerm2" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WeightedAverageGrantDateFairValuePriceGranted" name="WeightedAverageGrantDateFairValuePriceGranted" nillable="true" xbrli:periodType="duration" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="posc_SharesAuthorizedUnderEquityIncentivePlan" name="SharesAuthorizedUnderEquityIncentivePlan" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePrice" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardExercisePrice" nillable="true" xbrli:periodType="instant" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ShareBasedCompensationArrangementByShareBasedPaymentAwardContractualTerm" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardContractualTerm" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesGranted" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WeightedAverageRemainingContractualTermYearsOutstanding" name="WeightedAverageRemainingContractualTermYearsOutstanding" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="posc_NumberOfWarrantsExercisable" name="NumberOfWarrantsExercisable" nillable="true" xbrli:periodType="instant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WeightedaverageexercisePriceExercisable" name="WeightedaverageexercisePriceExercisable" nillable="true" xbrli:periodType="instant" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WeightedAverageRemainingContractualTermYearsExercisable" name="WeightedAverageRemainingContractualTermYearsExercisable" nillable="true" xbrli:periodType="duration" type="xbrli:durationItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WarrantsAndRightsExercisable" name="WarrantsAndRightsExercisable" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_NumberOfWarrantsGranted" name="NumberOfWarrantsGranted" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WeightedaverageexercisePriceGranted" name="WeightedaverageexercisePriceGranted" nillable="true" xbrli:periodType="duration" type="dtr-types:perShareItemType" substitutionGroup="xbrli:item" />
    <element id="posc_NumberOfWarrantsExercised" name="NumberOfWarrantsExercised" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_NumberOfWarrantsCancelledforfeited" name="NumberOfWarrantsCancelledforfeited" nillable="true" xbrli:periodType="duration" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" />
    <element id="posc_WarrantsDescription" name="WarrantsDescription" nillable="true" xbrli:periodType="duration" type="xbrli:stringItemType" substitutionGroup="xbrli:item" />
    <element id="posc_LeaseLiability" name="LeaseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredTaxAssetsStockBasedCompensation" name="DeferredTaxAssetsStockBasedCompensation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredTaxLiabilitiesRightofuseLiability" name="DeferredTaxLiabilitiesRightofuseLiability" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredTaxLiabilityValuationAllowance" name="DeferredTaxLiabilityValuationAllowance" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ValuationAllowance" name="ValuationAllowance" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_TotalIncomeTaxProvisionBenefit" name="TotalIncomeTaxProvisionBenefit" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_Subtotal" name="Subtotal" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_SubtotalInPercentage" name="SubtotalInPercentage" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="posc_IncomeTaxExpenseBenefitRate" name="IncomeTaxExpenseBenefitRate" nillable="true" xbrli:periodType="duration" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredTaxAssetsOperatingLossCarryforwardsFederal" name="DeferredTaxAssetsOperatingLossCarryforwardsFederal" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_FederalNolCarryforwards" name="FederalNolCarryforwards" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredTaxAssetsOperatingLossCarryforwardSubjectToExpiration" name="DeferredTaxAssetsOperatingLossCarryforwardSubjectToExpiration" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ChangeInValuationAllowance" name="ChangeInValuationAllowance" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_ResearchDevelopmentAndTechnologyTransferFeesMember" name="ResearchDevelopmentAndTechnologyTransferFeesMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DeferredRevenueByArrangementTableTextBlock" name="DeferredRevenueByArrangementTableTextBlock" nillable="true" xbrli:periodType="duration" type="dtr-types:textBlockItemType" substitutionGroup="xbrli:item" />
    <element id="posc_DebtInstrumentImputedInterestRatePercentage" name="DebtInstrumentImputedInterestRatePercentage" nillable="true" xbrli:periodType="instant" type="dtr-types:percentItemType" substitutionGroup="xbrli:item" />
    <element id="posc_StateIncomeTaxNetOfFederal" name="StateIncomeTaxNetOfFederal" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_FederalIncomeTaxBenefit" name="FederalIncomeTaxBenefit" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_Thereafter" name="Thereafter" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_OperatingLeasesFutureMinimumPaymentDueInFourYears" name="OperatingLeasesFutureMinimumPaymentDueInFourYears" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_OperatingLeasesFutureMinimumPaymentDueInThreeYears" name="OperatingLeasesFutureMinimumPaymentDueInThreeYears" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_OperatingLeasesFutureMinimumPaymentDueInTwoYears" name="OperatingLeasesFutureMinimumPaymentDueInTwoYears" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_OperatingLeasesFutureMinimumPaymentDueCurrent" name="OperatingLeasesFutureMinimumPaymentDueCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" />
    <element id="posc_BoardOfDirectorsMember" name="BoardOfDirectorsMember" nillable="true" xbrli:periodType="duration" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" />
</schema>
